This invention is most generally characterized as a research instrument. It is a device used in research in geology. More specifically, it is a device used in the field to measure physical properties of rocks and similar geological materials. Even more specifically it is a device used to measure the permeability of rocks and similar geological materials in their natural (field) setting.
The invention comprises a hand-held, hand-operated device used to determine the permeability of rock in its field or natural setting. A tube with an expandable stopper is inserted into a pre-drilled hole in the rock. A wheel element threaded on the tube is rotated to exert a force on a sleeve that contacts the stopper. The stopper expands in response to the force, thereby sealing the hole. A gas from under known pressure is introduced through the tube and a junction box that connects the device to an external source of the gas. A thin capillary tube is positioned in the tube and connected through the junction box to data recording and display equipment. The flow of gas at a steady state is subject to analysis that yields permeability of the rock.
The science of geology focuses on the understanding the physical and chemical nature and properties of the earth""s crust, specifically those strata at or below the surface. Characterizing the basic physical and chemical properties of these rocky strata, including those strata exposed at the earth""s surface, is fundamental to understanding, managing, and protecting geological resources such as minerals, fossil fuel reserves, and subsurface water resources, including water quality on which many human activities depend.
Permeability of rocks to fluids is an important, basic physical characteristic used to describe, distinguish, and classify numerous types of rocks and rocky strata. Permeability is an important physical property that influences how fluids of all types move into and through various rocky strata. In the face of justifiable, increasing concerns of pollution of sub-surface water resources and equally justifiable concerns related to decreasing supplies of fossil fuels, characterizing the strata through which water moves and through which pollutants may enter, as well as characterizing the strata in which fossil fuels are found, assumes importance other than basic scientific interest.
Unlike some sciences, field research is an essential element of basic research in geology. Obviously, considering the subject matter comprising geology, moving representative samples from a field site to the laboratory for study is commonly impractical, if not effectively impossible. Measurements made on relatively small samples removed from their natural settings may not reflect the characteristics of the materials in their natural state. Simple, cost effective devices to measure accurately the permeability of rocky materials in their natural setting are of immediate practical use and value, not only to the basic study of geology, but for the protection of certain natural resources.
Prior art reveals a variety of devices that are used for field determination of permeability of rocky strata. Although these devices to measure permeability may differ in structural detail, functionally they all are very similar, all involve the same basic concepts, and all suffer from the same general deficiencies.
In the most fundamental sense, permeability of a rocky material is determined by measuring the rate of flow of a fluid of known properties (often a gas) into the material with the fluid delivered under measured and controlled conditions. In the present application, the fluid used is a gas. When both the flow and pressure reach and maintain a stable (time-independent event) state, permeability may be determined. Devices for this procedure require a source of gas under pressure, a valve system to control the rate and pressure of gas delivery, and suitable devices to display flow rate and pressure. Such valve systems and devices are readily available. In addition a means to deliver the gas to the study material is required. This means is a tube commonly described as a probe, the distal end of which is adapted to form a seal between the surface of the rock and the probe interior.
With existing probe devices, the user manually applies pressure to the device to form the necessary seal between the probe and surface of the rock. A defective seal yields unreliable results because both the flow of the gas and pressure are affected to an unknown extent. The gas is delivered by mechanical means through the flow measuring means to the tube and through the tube to the tube/rock interface. The pressure at the distal end of the probe in relation to the flow of the gas is a measure of resistance to flow into the rock, or the permeability of the rock. By means well known to those skilled in the art, the flow and pressure readings are transformed into permeability values that in turn may be compared with other samples.
The greatest deficiencies of the prior art are found in aspects of the device described above: the seal at the interface between the distal end of the probe and the rock may be defective; measurements may vary as a result of the skill and experience of the individual using the device; fatigue and use in awkward positions may affect the quality of the seal, and permeability estimates are based on characteristics of the weathered surface of the rock, and this surface generally is recognized by those skilled in the art as not being fully representative of the parent, unweathered rock material.